Many software applications now require to be registered with a registration authority, usually associated with the provider of the software, either prior to any use or prior to being able to utilise the full functionality of the software application. One piece of information which is commonly required by the registration authority is an email address for the user of the software. This may be required for the operation of the software application, to help prevent software piracy, or simply for marketing purposes. However, the verification of the submitted email address by the registration authority is a problem.
A software application for which it is important that the correct email address for the user is registered is an encrypted email application which utilises asymmetric encryption with the private and public keys for a user being calculated using the email address for the user. This allows a public key associated with the recipient of an electronic mail message to be used by the sender to encrypt the message. The resultant encrypted message can only be decrypted using a private key which is different from the corresponding public key, with access to the private key being controlled by the recipient of the electronic mail message.
As well as ensuring that a message is only read by a desired recipient, public key cryptography also enables the author of a message and the message content to be verified. In particular a digital signature can be added to the message, the digital signature being formed by encrypting a one-way hash of the message using the private key of the sender. The recipient of the message is then able to decrypt the digital signature using the public key of the sender and compare the result with a one-way hash of the received message to verify the identity of the sender and the content of the message.